Wafer cleaning

ABSTRACT

Semiconductor wafers are cleaned using megasonic energy to agitate cleaning fluid applied to the wafer. A source of energy vibrates an elongated probe which transmits the acoustic energy into the fluid. The probe has a solid cleaning rod and a flared or stepped rear base. In one form, the probe is made of one piece, and in another, the rod fits into a socket in the base. This enables a rod to be made of material which is compatible with the cleaning solution, while the base may be of a different material. A heat transfer member acoustically coupled to the probe base and to a transducer conducts heat away from the transducer. A housing for the heat transfer member and the transducer supports those components and provides means for conducting coolant through the housing to control the temperature of the transducer. In another arrangement, an end of the housing is coupled between the transducer and the probe. In one arrangement, fluid is sprayed onto both sides of a wafer while a probe is positioned close to an upper side. In another arrangement, a short probe is positioned with its end face close to the surface of a wafer, and the probe is moved over the wafer as it rotates. The probe may also be positioned through a central hole in a plurality of discs to clean a group of such elements at one time.

RELATED APPLICATIONS

[0001] This application is a continuation of U.S. application Ser. No.09/953,504, filed Sep. 13, 2001, which is a continuation of U.S.application Ser. No. 09/643,328, filed Aug. 22, 2000, now U.S. Pat. No.6,295,999, issued Oct. 2, 2001, which is a continuation of U.S.application Ser. No. 09/057,182, filed Apr. 8, 1998, now U.S. Pat. No.6,140,744, issued Oct. 31, 2000, which is a continuation-in-part of U.S.application Ser. No. 08/724,518, filed Sep. 30, 1996, now U.S. Pat. No.6,039,059, issued Mar. 21, 2000.

FIELD OF THE INVENTION

[0002] This invention relates to an apparatus and method for cleaningsemiconductor wafers or other such items requiring extremely high levelsof cleanliness.

BACKGROUND OF THE INVENTION

[0003] Semiconductor wafers are frequently cleaned in cleaning solutioninto which megasonic energy is propagated. Megasonic cleaning systems,which operate at a frequency over twenty times higher than ultrasonic,safely and effectively remove particles from materials without thenegative side effects associated with ultrasonic cleaning.

[0004] Megasonic energy cleaning apparatuses typically comprise apiezoelectric transducer coupled to a transmitter. The transducer iselectrically excited such that it vibrates, and the transmittertransmits high frequency energy into liquid in a processing tank. Theagitation of the cleaning fluid produced by the megasonic energy loosensparticles on the semiconductor wafers. Contaminants are thus vibratedaway from the surfaces of the wafer. In one arrangement, fluid entersthe wet processing container from the bottom of the tank and overflowsthe container at the top. Contaminants may thus be removed from the tankthrough the overflow of the fluid and by quickly dumping the fluid.

[0005] A gas impingement and suction cleaning process forelectrostatographic reproducing apparatuses which utilizes ultrasonicenergy and air under pressure is disclosed in U.S. Pat. No. 4,111,546,issued to Maret.

[0006] A process for cleaning by cavitation in liquefied gas isdisclosed in U.S. Pat. No. 5,316,591, issued to Chao et al. Undesiredmaterial is removed from a substrate by introducing a liquefied gas intoa cleaning chamber and exposing the liquefied gas tocavitation-producing means. The shape of the horn to provide thecavitation is not disclosed in detail and does not concentrate the sonicagitation to a particular location within the cleaning vessel.

[0007] In U.S. Pat. No. 4,537,511, issued to Frei, an elongated metaltube in a tank of cleaning fluid is energized in the longitudinal wavemode by a transducer that extends through a wall of the tank and isattached to the end of the tube. In order to compensate for relativelyhigh internal losses, the radiating arrangement uses a relativelythin-walled tubular member.

[0008] A need exists for an improved apparatus and method which can beused to clean semiconductor wafers.

SUMMARY OF THE INVENTION

[0009] The above-referenced parent patent application claims variousforms of the invention. The present application is directed toadditional embodiments of the invention. This includes a housing havingan end wall with a vibrator or transducer, such as a piezoelectrictransducer coupled to an interior surface of the end wall, while anelongated probe has an end coupled to an exterior surface of the housingend wall. The transducer when energized propagates megasonic energythrough the housing end wall and into the probe. The housing ispreferably made of aluminum of other material having good thermalconductivity so that heat generated by the transducer is dissipatedthrough the housing.

[0010] A liquid coolant passage is formed in heat transfer relation withthe housing. Preferably, this is accomplished by positioning a heattransfer member in the housing in a manner to form the passage incombination with an interior wall of the housing. Coolant is thenconducted through this passage to provide the desired cooling effect.The transducer is sealed from the liquid coolant, but nitrogen or othergas may be conducted into the housing, preferably through the heattransfer member, to provide gaseous cooling for the transducer.

[0011] Preferably, the probe is coupled to the housing by positioning alayer of viscous material between the housing end wall and the probe andpressing the probe against the housing end wall. The pressing force isprovided by compressing a spring against the probe with a springretainer plate which is clamped to the housing. In addition, an O-ringsurrounds the interface between the probe and the housing end wall toconfine the viscous material and to center the probe, and is clamped inposition by a retaining ring mounted to the housing end wall.

[0012] A significant advantage of this embodiment is that the housingend wall through which the vibrational energy is transmitted is muchthinner than the heat transfer member which is positioned between theprobe and the transducer in the other embodiments. This reduced massallows increased energy to be transmitted to the probe with the sameelectrical input. The thin wall has fewer internal reflections of energyand makes tuning the transducer easier. Nevertheless, approximately thesame cooling capacity is provided with a housing and a heat transfermember having a size comparable to that of the other embodiments.

[0013] In another embodiment, a thin wall of a heat transfer member issandwiched between the transducer and the probe. Surrounding the thinwall is an elongated annular wall of the heat transfer member, which inturn fits snugly within a surrounding cylindrical housing. A channelformed in the exterior surface of the annular wall of the heat transfermember forms a coolant passage in combination with the housing. AnO-ring surrounding the base of the probe is held in position by aretaining ring fastened to the end of the housing. Since the base orrear of the probe extends into the housing, the retainer ring includes acylindrical portion that extends into the housing to engage the O-ring.An advantage of this embodiment of the invention is that the megasonicenergy can be efficiently transmitted by the transducer through the thinwall of the heat transfer member into the probe, while at the same timeproviding excellent cooling characteristics because of a direct pathfrom the transducer through the heat transfer member to the coolingfluid passage.

[0014] Another aspect of the invention that applies to all theembodiments discussed above, as well as those in the parent application,is a probe made of a base having a socket formed therein for receivingan elongated rod portion preferably having a constant cross-section. Thebase and rod are coupled in a manner to efficiently transmit themegasonic energy from the base to the rod. An advantage of thisarrangement is that a single base can be used for rods of differentmaterials and lengths which are to be contacted by a cleaning fluid. Forexample, a quartz base may be used for many applications, while a rod ofdifferent material may be used with a solution containing hydrofluoricacid, which is not compatible with quartz. Also, some materials such asvitreous carbon can withstand most cleaning solutions but the materialis presently only readily available in constant diameter rod form.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a side elevational view of one embodiment of themegasonic energy cleaning system of the present invention.

[0016]FIG. 2 is a side cross-sectional view of the system shown in FIG.1.

[0017]FIG. 3 is an exploded perspective view of the probe assembly shownin FIG. 1.

[0018]FIG. 4 is a side view of an alternative probe in accordance withthe present invention.

[0019]FIGS. 5a-5 c are alternative probe tips which may be used inconnection with the present invention.

[0020]FIG. 6 is a schematic view of the probe of the present inventionused with cleaning fluid being sprayed onto the upper surface of awafer.

[0021]FIG. 7 is a cross-sectional view on line 7-7 of FIG. 6.

[0022]FIG. 8 is a schematic view of the probe cleaning both surfaces ofa wafer.

[0023]FIG. 9 is a schematic view of the probe of FIG. 1 extendingthrough discs to be cleaned.

[0024]FIG. 9a is a fragmentary, cross sectional view of a cap for aprobe tip.

[0025]FIG. 9b is a fragmentary, cross sectional view of another probetip cap.

[0026]FIG. 10 is a schematic view of a probe vertically oriented withrespect to a wafer.

[0027]FIG. 11 a side elevational, partially sectionalized view ofanother embodiment of the invention having an alternate means ofcoupling the probe to a support.

[0028]FIG. 12 is a side elevational, partially sectionalized view ofanother embodiment of the invention having an alternate means ofmounting the probe to the housing.

[0029]FIG. 13 is a side elevational, partially sectionalized view ofanother embodiment of the invention having an alternate arrangement formounting the probe and an alternate probe construction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0030] FIGS. 1-3 illustrate a megasonic energy cleaning apparatus madein accordance with the present invention with an elongated probe 104inserted through the wall 100 of a processing tank 101. As seen, theprobe is supported in cantilever fashion on one end exterior of thecontainer. A suitable O-ring 102, sandwiched between the probe 104 andthe tank wall, provides a proper seal for the processing tank 101. Aheat transfer member 134, contained within a housing 120, isacoustically and mechanically coupled to the probe 104. Also containedwithin the housing 120 is a piezoelectric transducer 140 acousticallycoupled to the heat transfer member 134. Electrical connectors 142, 154,and 126 are connected between the transducer 140 and a source ofacoustic energy (not shown).

[0031] The housing supports an inlet conduit 124 and an outlet conduit122 for coolant and has an opening 152 for electrical connectors. Thehousing is closed by an annular plate 118 with an opening 132 for theprobe. The plate in turn is attached to the tank.

[0032] Within the processing tank 101, a support or susceptor 108 ispositioned parallel to and in close proximity to the probe 104. Thesusceptor 108 may take various forms, the arrangement illustratedincluding an outer rim 108 a supported by a plurality of spokes 108 bconnected to a hub 108 c supported on a shaft 110, which extends througha bottom wall of the processing tank 101. Outside the tank 101, theshaft 110 is connected to a motor 112.

[0033] The elongated probe 104 is preferably made of a relatively inert,non-contaminating material, such as quartz, which efficiently transmitsacoustic energy. While utilizing a quartz probe is satisfactory for mostcleaning solutions, solutions containing hydrofluoric acid can etchquartz. Thus, a probe made of sapphire silicon carbide, boron nitride,vitreous carbon, glassy carbon coated graphite, or other suitablematerials may be employed instead of quartz. Also, quartz may be coatedby a material that can withstand HF such as silicon carbide or vitreouscarbon.

[0034] The probe 104 comprises a solid, elongated, constantcross-section spindle-like or rod-like cleaning portion 104 a, and abase or rear portion 104 b. The cross-section of the probe is preferablyround and advantageously, the diameter of the cleaning portion of theprobe is smaller in diameter than the rear portion of the probe. In aprototype arrangement the area of the rear face of the rear portion 104b is 25 times that of the tip face of portion 104 a. Of course,cross-sectional shapes other than circular may be employed.

[0035] A cylindrically-shaped rod portion 104 a having a small diameteris desirable to concentrate the megasonic energy along the length of therod 104 a. The diameter of the probe, however, should be sufficient towithstand mechanical vibration produced by the megasonic energytransmitted by the probe. Preferably, the radius of the rod portion 104b should be equal to or smaller than the wavelength of the frequency ofthe energy applied to it. This structure produces a desired standingsurface wave action which directs energy radially into liquid contactingthe rod. In a prototype, the radius of the cylindrical portion of theprobe contained within the tank was approximately 0.2 of an inch andoperated at a wave length of about 0.28 of an inch. This produced 3 to 4wave lengths per inch along the rod length and has provided goodresults.

[0036] The probe cleaning portion 104 a should be long enough so thatthe entire surface area of the wafer is exposed to the probe duringwafer cleaning. In a preferred embodiment, because the wafer is rotatedbeneath the probe, the length of the cleaning portion 104 b should belong enough to reach at least the center of the wafer. Therefore, as thewafer is rotated beneath the probe, the entire surface area of the waferis close to the probe. Actually, the probe could probably functionsatisfactorily even if it does not reach the center of the wafer sincemegasonic vibration from the probe tip would provide some agitationtowards the wafer center.

[0037] The length of the probe is also determined by a predeterminednumber of wavelengths usually in increments of half wavelengths of theenergy applied to the probe. In one embodiment, the length of the probecleaning portion 104 a equals nineteen wavelengths of the appliedenergy. Due to variations in transducers, it is necessary to tune thetransducer to obtain the desired wavelength, so that it works at itsmost efficient point.

[0038] The rear probe portion 104 b, which is positioned exterior thetank, flares to a diameter larger than the diameter of the cleaningportion 104 a. In a first embodiment of the present invention, shown inFIGS. 1-3, the diameter of the cross-section of the rear portion of theprobe gradually increases to a cylindrical section 104 d. The largesurface area at the end of the rear portion 104 d is advantageous fortransmitting a large amount of megasonic energy which is thenconcentrated in the smaller diameter section 104 a.

[0039] As illustrated in FIG. 4, in an alternative embodiment of thepresent invention, the diameter of the cross-section of the rear portionof the probe increases in stepped increments, rather than gradually. Thestepped increments occur at wavelength multiples to efficiently transmitthe megasonic energy. For example, in one embodiment, the thinnestportion 158 of the probe has a length of approximately nineteenwavelengths, the next larger diameter portion 160 is about threewavelengths in axial length and the largest diameter portion 162 isabout four wavelengths in axial length. The goal is to simulate theresults obtained with the tapered arrangement of FIG. 1.

[0040]FIGS. 5a-5 c depict further embodiments for the tip of the probe.The different probe tips may help cover a portion of the wafer surfacethat otherwise would not be covered by a flat probe end 157. The probemay have a conical tip 164, an inverted conical tip 166, or a roundedtip 168.

[0041] The probe base 104 d is acoustically coupled to a heat transfermember 134 and is physically supported by that member. The probe endface is preferably bonded or glued to the support by a suitable adhesivematerial. In addition to the bonding material, a thin metal screen 141,shown in FIG. 3, is sandwiched between the probe end and the member 134.The screen with its small holes filled with adhesive provides a morepermanent vibration connection than that obtained with the adhesive byitself. The screen utilized in a prototype arrangement was of theexpanded metal type, only about 0.002 inch thick with flattened strandsdefining pockets between strands capturing the adhesive. The adhesiveemployed was purchased from E. V. Roberts in Los Angeles and formed by aresin identified as number 5000, and a hardener identified as number 61.The screen material is sold by a U.S. company, Delkar. The probe canpossibly be clamped or otherwise coupled to the heat transfer member solong as the probe is adequately physically supported and megasonicenergy is efficiently transmitted to the probe.

[0042] As another alternative, the screen 141 may be made of a beryliumcopper, only about 0.001 inch thick, made by various companies usingchemical milling-processes. One available screen holes for confining theresin that are larger than that of the Delkar.

[0043] The heat transfer member 134 is made of aluminum, or some othergood conductor of heat and megasonic energy. In the arrangementillustrated, the heat transfer member is cylindrical and has an annulargroove 136, which serves as a coolant duct large enough to provide anadequate amount of coolant to suitably cool the apparatus. Smallerannular grooves 138, 139 on both sides of the coolant groove 136 arefitted with suitable seals, such as O-rings 135, 137 to isolate thecoolant and prevent it from interfering with the electrical connectionsto the transducer 140.

[0044] The transducer 140 is bonded, glued, or otherwise acousticallycoupled to the rear flat surface of the heat transfer member 134. Asuitable bonding material is that identified as ECF 550, available fromAblestick of Gardena, Calif. The transducer 140 is preferably discshaped and has a diameter larger than the diameter of the rear end ofthe probe section 104 d to maximize transfer of acoustic energy from thetransducer to the probe. The heat transfer member is preferablygold-plated to prevent oxidizing of the aluminum and, hence, providebetter bonding to the transducer and the probe. The member 134 shouldhave an axial thickness that is approximately equal to an even number ofwave lengths or half wave lengths of the energy to be applied to theprobe.

[0045] The transducer 140 and the heat transfer member 134 are bothcontained within the housing 120 that is preferably cylindrical inshape. The heat transfer member is captured within an annular recess 133in an inner wall of the housing 120.

[0046] The housing is preferably made of aluminum to facilitate heattransfer to the coolant. The housing has openings 144 and 146 for theoutlet 122 and the inlet conduit 124 for the liquid coolant. On itsclosed end, the housing 134 has an opening 152 for the electricalconnections 126 and 154. Openings 148, 150 allow a gaseous purge toenter and exit the housing 120.

[0047] An open end of the housing 120 is attached to the annular plate118 having the central opening 132 through which extends the probe rearsection 104 d. The annular plate has an outer diameter extending beyondthe housing 120 and has a plurality of holes organized in two ringsthrough an inner ring of holes 131, a plurality of connectors 128, suchas screws, extend to attach the plate 118 to the housing 120. Theannular plate 118 is mounted to the tank wall 100 by a plurality ofthreaded fasteners 117 that extend through the outer ring of plate holes130 and thread into the tank wall 100. The fasteners also extend throughsleeves or spacers 116 that space the plate 118 from the tank wall. Thespacers position the transducer and flared rear portion 104 b of theprobe outside the tank so that only the cleaning portion of the probeand the probe tip extend into the tank. Also, the spacers isolate theplate 118 and the housing from the tank somewhat, so that vibration fromthe heat transfer member, the housing and the plate to the wall isminimized.

[0048] The processing tank 101 is made of material that does notcontaminate the wafer. The tank should have an inlet (not shown) forintroducing fluid into the tank and an outlet (not shown) to carry awayparticles removed from the article.

[0049] As the size of semiconductor wafers increases, rather thancleaning a cassette of wafers at once, it is more practical and lessexpensive to use a cleaning apparatus and method that cleans a singlewafer at a time. Advantageously, the size of the probe of the presentinvention may vary in length depending on the size of the wafer to becleaned.

[0050] A semiconductor wafer 106 or other article to be cleaned isplaced on the support 108 within the tank 101. The wafer is positionedsufficiently close to the probe so that the agitation of the fluidbetween the probe and the wafer loosens particles on the surface of thewafer. Preferably, the distance between the probe and surface of thewafer is no greater than about 0.1 of an inch.

[0051] The motor 112 rotates the support 108 beneath the probe 104 sothat the entire upper surface of the article is sufficiently close tothe vibrating probe 104 to remove particles from the surface of thearticle. To obtain the necessary relative movement between the probe andthe wafer 106, an arrangement could be provided wherein the wafer ismoved transversely beneath the probe. Also, an arrangement could beprovided wherein the support 108 remains in place while a probe movesabove the surface of the wafer 106.

[0052] When the piezoelectric transducer 140 is electrically excited, itvibrates at a high frequency. Preferably the transducer is energized atmegasonic frequencies with the desired wattage consistent with the probesize length and work to be performed. The vibration is transmittedthrough the heat transfer member 134 and to the elongated probe 104. Theprobe 104 then transmits the high frequency energy into cleaning fluidbetween the probe and the wafer. One of the significant advantages ofthe arrangement is that the large rear portion of the probe canaccommodate a large transducer, and the smaller forward probe portionconcentrates the megasonic vibration into a small area so as to maximizeparticle loosening capability. Sufficient fluid substance between theprobe and the wafer will effectively transmit the energy across thesmall gap between the probe and the wafer to produce the desiredcleaning. As the surface area of the wafer 106 comes within closeproximity to the probe 104, the agitation of the fluid between the probe104 and the wafer 106 loosens particles on the semiconductor wafer 106.Contaminants are thus vibrated away from the surfaces of the wafer 106.The loosened particles may be carried away by a continued flow of fluid.

[0053] Applying significant wattage to the transducer 140 generatesconsiderable heat, which could present damage to the transducer 140.Therefore, coolant is pumped through the housing 120 to cool the member134 and, hence, the transducer.

[0054] A first coolant, preferably a liquid such as water, is introducedinto one side of the housing 120, circulates around the heat transfermember 134 and exits the opposite end of the housing 120. Because theheat transfer member 134 is made of a good thermal conductor,significant quantities of heat may be easily conducted away by theliquid coolant. The rate of cooling can, of course, be readily monitoredby changing the flow rate and/or temperature of the coolant.

[0055] A second, optional coolant circulates over the transducer byentering and exiting the housing 120 through openings 148, 150 on theclosed end of the housing. Due to the presence of the transducer 140 andthe electrical wiring 142, 154, an inert gas such as nitrogen is used asa coolant or as a purging gas in this portion of the housing.

[0056] An alternative arrangement for coupling the probe end 104 b tothe member 134 is illustrated in FIG. 11. Instead of having the probebonded to the member 134, a so-called vacuum grease is applied to thescreen 141, and the probe is pressed against the member 134 by a coilspring 143. Vacuum grease is a viscous grease which can withstandpressures on opposite sides of a joint without leaking or being readilydisplaced. In a prototype arrangement, the combination of the grease andthe metal spring provided a reliable acoustic coupling. As may be seenin FIG. 11, the housing 120 instead of being mounted directly to theplate 118, is mounted by standoffs 16 to the plate 118. The sleeves 116and the fasteners 117 are shorter than that shown in FIG. 2, such thatthe plate 118 surrounds the tapered portion of the probe. This leaves agap between the housing 120 and the plate 118. The coil spring 143 ispositioned in this gap and compressed between the plate 118 and thetapered portion of the probe. Thus, the spring presses the probe towardthe member 134. This arrangement acoustically couples the probe to theheat transfer member 134. A Teflon sleeve 149 is preferably positionedover the first coil of the spring 143 adjacent the probe so that themetal spring does not damage the quartz probe.

[0057] An arrangement is illustrated in FIG. 6, wherein the probeassembly of FIG. 1 is shown in conjunction with a tank 200 which is openon its upper end and has a drain line 202 in its lower end. The probe104 is shown extending through a slot 203 into the tank above a wafer106 mounted on a suitable support 208 including an annular rim 208 a, aplurality of spokes 208 b, joined to a hub 208 c positioned on the upperend of a shaft 210 rotated by a motor 212.

[0058] In use, deionized water or other cleaning solution is sprayedonto the upper surface of the wafer from a nozzle 214 while the probe104 is being acoustically energized. The liquid creates a meniscus 115between the lower portion of the probe and the adjacent upper surface ofthe rotating wafer. This is schematically illustrated in FIG. 7. Theliquid provides a medium through which the megasonic energy istransmitted to the surface of the wafer to loosen particles. Theseloosened particles are flushed away by the continuously flowing sprayand the rotating wafer. When the liquid flow is interrupted, a certainamount of drying action is obtained through centrifical force of theliquid off of the water.

[0059] The probe assembly may be conveniently mounted on a suitablesupport, schematically illustrated at 216. The support is capable ofpivoting the assembly upwardly, as indicated by the arrow in FIG. 6, tofacilitate the installation and removal of wafers. Alternatively, theslot 203 may instead be formed as a hole, closed at the top, and theprobe may be moved radially in and out.

[0060]FIG. 8 illustrates an alternative or addition to the arrangementof FIG. 7 wherein both the lower and upper sides of a wafer are cleaned.A spray nozzle 254 extends through a side wall of a tank 200 and isangled upwardly slightly so that cleaning fluid may be sprayed betweenthe spokes 208 b and onto the lower surface of a wafer 106 and isdirected radially inwardly so that as the wafer rotates, the entirelower surface is sprayed with the fluid. The wafer is subjected tomegasonic energy by the probe 104 in the same manner as described abovein connection with FIG. 6. This agitation vibrates the wafer as well asthe fluid on the lower surface of the wafer which is radially alignedwith the probe as the wafer rotates. This agitation loosens particles onthe lower surface of the wafer, and the particles are flushed away withthe fluid which falls or drips from the lower surface of the wafer.

[0061] Various fluids may be employed as the spray applied to the waferin FIGS. 6 and 8. In addition to liquid or high pressure gas, so-calleddry ice snow may be applied. Va-Tran Systems, Inc. of Chula Vista,Calif. markets a product under the trademark SNO GUN for producing andapplying such material. A major advantage of that approach is that thereis no disposal problem after cleaning. Contamination is carried awayfrom the clean surface in a stream of inert, harmless vapor. Disposalcosts of cleaning media are eliminated. Advertising literature regardingthe SNO GUN product states that cleaning with dry ice snow removesparticles more thoroughly than blowing with dry nitrogen. It is saidthat the device removes even sub-micron particles as tiny as 0.2microns, which are difficult or impossible to remove with a nitrogenjet. Such technology is further described in U.S. Pat. No. 5,364,474,which is incorporated herein by reference.

[0062] Referring to FIG. 9, the probe assembly of FIG. 1 is shownmounted to a wall of a tank 300. The probe 104 extends generallyhorizontally through central openings in a plurality of verticallyorientated substrates such as “compact discs” 302. The discs may bemounted in a cassette immersed in the tank with the holes in the discsaligned with the probe. The cassette carrying the discs can then bemoved laterally so that the probe extends through the holes in thediscs, without actually contacting the discs. The tank is filled withliquid, such as deionized water to completely cover the discs. The probeis then vibrated by megasonic energy in the manner described above inconnection with FIG. 1. The agitation produced by the probe istransmitted into the cleaning liquid between the discs to loosenparticles on the surfaces of the discs. The energy propagates radiallyoutward from the probe such that both sides of each disc are exposed tosuch energy. Cleaning liquid may be introduced into the container incontinuous flow and allowed to overflow the upper end of the containerto carry away loosened particles.

[0063] Because some megasonic energy will be transmitted through the endof the probe with the probe tip immersed in the liquid, a small cap 306is positioned on the tip of the probe with the cap containing an airspace 308 between two glass walls 306 a and 306 b, as shown in FIG. 9a.Since megasonic energy does not travel through ambient air to anysignificant degree, the cap prevents the loss of energy through the endof the probe. An alternative cap 310 shown in FIG. 9b employs a shortsection of glass tubing 212 attached to the end of the probe. As seen,the outer diameter of the tube is equal to the outer diameter of theprobe, and the outer end of the tube spaced from the probe is closed bya disc 314.

[0064]FIG. 10 illustrates another embodiment of the probe of theinvention. A probe assembly 400 is shown which is similar to theassembly of FIG. 1 except that the probe 404 is much shorter than theprobe 104 in FIG. 1. In addition, the assembly 400 is oriented with theprobe extending generally vertically, generally perpendicular to thesurface of the horizontal wafer 106. Cleaning fluid is applied to theupper surface of the wafer, and the lower tip of the probe is in contactwith this fluid. Consequently, megasonic energy is transmitted throughthis medium onto the surface of the wafer causing loosening ofparticles. Since the sides of the probe are not exposed to this medium,there is no appreciable megasonic energy transmitted from the verticalsides of the probe. Instead, such megasonic energy is concentrated intothe tip. The tip can be moved radially with respect to the wafer as thewafer rotates so as to apply megasonic energy to the entire surface ofthe wafer. Alternatively, the probe may traverse the entire uppersurface. Any suitable support 410 containing a mechanism to provide thedesired movement may be employed.

[0065] As mentioned above, the preferred form of the probe assemblyincludes a probe made of inert material such as quartz and a heattransfer member coupled to the rear of the probe made of a good heatconducting material such as aluminum. Since it is the cylindricalportion of the probe which is in contact with the cleaning fluid and ispositioned adjacent the wafer, an alternative arrangement could bedevised wherein a forward portion, such as section 104 a in FIG. 1 couldbe made of the inert material and the rear portion 104 b could be madeof aluminum and hence could be made as one piece with the heat transfermember 134. This of course means that the joint between the twocomponents would be at the rear of the cylindrical portion 104 a. Whilesuch a bonding area would not be as strong as the arrangementillustrated in FIG. 1, it may be useful in certain situations.

[0066] In the other direction, there may be some applications in whichit is not necessary to employ quartz or other such inert material forthe probe. Instead, the entire probe could be made of aluminum or othersuch material. In that situation, the heat transfer member could then bemade as a one-piece unit with the probe. Also, with a metal probe it maybe practical to spray the cleaning fluid through the probe itself. Forexample in the arrangement of FIG. 10, fluid inlet could be located inthe side of the large diameter end of the probe and an outlet can belocated in the end face of the small diameter probe end. The fluid wouldalso serve as a coolant to cool the transducer, particularly if dry icesnow were employed.

[0067] The embodiment of FIG. 12 has a number of similarities to theother embodiments, but has some important distinctions. That arrangementincludes a cup-shaped housing 520 similar to the housing 120 in FIG. 2,but inverted with respect to the housing 120. The housing 520 includes aclosed end wall 520 a having a surface 520 b facing the interior of thehousing 520 and having an exterior surface 520 c facing away from thehousing. Coupled to the interior end wall surface 520 b is a disc-shapedtransducer 540 analogous to the transducer 140 referred to above inconnection with FIGS. 2 and 3. The transducer 540 is preferably bondedto the wall surface 520 b in the same manner mentioned above inconnection with FIGS. 2 and 3.

[0068] The large end 504 b of a probe 504 is acoustically coupled to thehousing end wall exterior surface 520 c. The acoustic coupling isaccomplished by the use of a coil spring 543 surrounding the probe 504and reacting against the spring retainer plate 518 to press the largeend 504 b of the probe towards the housing end wall 520 a. As discussedin connection with FIG. 3, a screen 141, together with an appropriateviscous material, is sandwiched between the large end of the probe andthe end wall 520 a. The coil spring adjacent the large end of the probehas a sleeve or sleeve portions 544 made of a material which will notdamage the probe. The O-ring is held in place and compressed against theend wall 520 a and the probe by a retainer ring 519 having a surface 519a which presses against the O-ring. The O-ring thus prevents the escapeof the viscous material from between the probe and the housing end wall,and centers the probe. The retainer ring is attached to the housing by aplurality of bolts 525 which extend through the retainer ring and threadinto the housing. The spring 543 is captured and compressed by areaction plate 518 which surrounds the probe and is attached to thehousing by a plurality of fasteners 528 which thread into the retainerring 519 and are spaced from it by sleeves 516 surrounding the fasteners528. For convenience of illustration, the fasteners 525 and 528 are allshown in the same plane in FIG. 12. In actual practice, the fasteners528 would preferably be on the same bolt hole diameter as the fasteners525, and they of course would be spaced with respect to the fasteners525. Also, the fasteners would not necessarily be spaced 180E apart asillustrated, but would be spaced in whatever manner is practical.

[0069] Positioned within the cup-shaped housing 520 is an annular heattransfer member 534 which has an external diameter sized to fit snuglywithin the housing 520. An annular groove 536 in the exterior of theheat transfer member 534, creates a liquid cooling channel incombination with the inner surface of the housing 520. A pair of O-rings537 that fit within annular grooves in the heat transfer member seal thecoolant channel 536 so that the remainder of the interior of the housingis sealed from the liquid. This prevents interference with theelectrical energy being supplied to the transducer. Further, transducervibration energy is not dissipated into the interior of the housing, butinstead is transmitted into the housing end wall 520 a and into theprobe 504. The heat transfer member 534 is axially captured within thehousing by means of an annular shoulder 520 d and by a housing end plate560. A plurality of fasteners 528 connect the plate 560 to the housing.A liquid coolant inlet 562 a is mounted in an opening in the end plate560 and threads into a passage 519 in the heat transfer member thatextends axially and then radially into the annular channel 536. Asimilar outlet fitting 562 b mounts in the end plate 560 diametricallyopposed from the 562 a fitting, and threads into another passage 519that extends axially and radially into the channel 536.

[0070] A plurality of axially extending bores 563 are also formed in theheat transfer member 534, aligned with gas inlets 561 formed in theplate 560. The inlets 561 and bores 563 are shown in the same plane withthe passages 519 for convenience. In actual practice, the bores 563would preferably not be in the same plane as the passages 519, andinstead would be circumferentially offset, and could also be formed inthe same circle around the center of the heat transfer member 534. Theinlets 561 through the end plate 560 for the fittings 562 a and 562 bwould likewise be moved to be aligned with the passages 563.

[0071] The electrical connection for the transducer 540 is illustratedby the wire 554, although the more complete connection would be as shownin FIG. 3. That wire extends through a fitting 528 which in turn isconnected to an electrical cord 526.

[0072] In operation, there are a number of advantages to the embodimentillustrated in FIG. 12. By coupling the transducer and the probe to thehousing end wall, more energy may be transmitted to the probe than withthe corresponding amount of power applied to the transducer in thearrangement of FIG. 2, inasmuch as the housing end wall has less massthan the mass of the heat transfer member 140 shown in FIG. 3. Whilesome energy is lost into the other portions of the housing, there is anet increase in efficiency. The relatively thin end wall has fewerinternal energy reflections than a thicker wall simply because of thereduced mass. However, in addition the housing end wall does not havethe discontinuities caused by the grooves in the heat transfer member ofFIG. 2, or by the O-ring in the grooves.

[0073] By making the housing 520 of aluminum or other material which isa relatively good thermal energy conductor, the heat generated by thetransducer can be readily dissipated with the arrangement of FIG. 12.The heat transfer member 534 can be made of the desired axial lengthwithout concern for its mass because it is not to be vibrated as in thearrangement of FIG. 2. The cooling liquid enters through the fitting 562a, flows axially and then radially into the channel 536, where it splitsinto two branch flows in opposite directions, that meet on the otherside of the heat transfer member and flow out the fitting 562 b.

[0074] Similarly, cooling gas such as nitrogen can be connected to oneor more of the bores 563 in the heat transfer member and into thecentral area of the housing. The gas is exhausted through one of thebores 563 leading to a second outlet 561 b. Two passages 563 areillustrated in FIG. 12. Three are preferable, but more or less may beutilized if desired. To perform an additional function, bolts may bethreaded into the bores 563 to assist in withdrawing the heat transfermember from the housing.

[0075] The assembly illustrated in FIG. 12 may be used in connectionwith a wall mounted arrangement such as that shown in FIG. 1, or may beused with a system such as that as illustrated in FIG. 8, wherein theprobe assembly is moved into or out of position with respect to a waferto facilitate insertion and removal of wafers. As mentioned above, sucha probe may be moved out of the way by mounting it on a bracket thatwill pivot it in the direction of the arrow 218 shown in FIG. 8, or itmay be on a track arrangement (not shown) which will move it radiallyinwardly and outwardly with respect to the wafer and its supportingmember. The assembly of FIG. 12 may be mounted to these other structuresin any suitable fashion, such as by making connections to the end plate560.

[0076] The arrangement of FIG. 13 includes a generally tubular orcylindrical housing 620. Positioned within the housing is a heattransfer member 634 having an outer annular wall 634 a which fits snuglywithin a surrounding annular wall of the housing 620. The heat transfermember 634 has an annular channel 636 formed in its outer surface thatfaces the surrounding housing wall to form a coolant passage. A coolantinlet 644 in the housing wall leads into the passage and an outlet 646on the opposite side of the housing leads out of the passage.

[0077] As seen in FIG. 13, the heat transfer member 634 has somewhat ofan H-shaped cross section created by a central disc-shaped wall 634 bintegrally formed with the surrounding annular wall 634 a. As seen, thecentral wall 634 b is relatively thin and it is radially aligned withthe surrounding coolant passage 636. The heat transfer member is axiallycaptured within the housing by an internal shoulder on one end of thehousing and by an end plate 660 on the other end.

[0078] A piezoelectric transducer 640 is acoustically coupled to oneside of the central wall 634 b, such as in the same manner discussedabove in connection with the other embodiments. A probe 604 isacoustically coupled to the other side of the central wall 634 b. Again,this may be done in various ways, such as the screen and greasetechnique discussed above. An O-ring 621 surrounds the base of the probeand is compressed against the probe and the central wall 634 b by acylindrical portion of an end member 619 having a flange attached to theend of the housing 620. The O-ring confines the coupling grease andhelps center the probe 604. The probe is pressed against the centralwall 634 b by a spring 643 compressed between an annular spring retainerplate 18 and the probe 604.

[0079] The housing and heat transfer member illustrated in FIG. 13 maybe used with the probes illustrated in the above-mentioned embodiments,but it is illustrated in FIG. 13 with an alternate probe construction.Instead of having the probe made of one piece, it is formed in separateportions including a base 605 adjacent the central wall 634 b of theheat transfer member, and an elongated cleaning rod 606. The base 605has a cylindrical exterior with a reduced diameter portion 605 a on theend spaced from the central wall 634 b. One end of the spring 643surrounds the base portion 605 a and engages the shoulder on the base605 adjacent the portion 605 a. The rod 606 of the probe fits within acentral socket formed in the base 605. It is bonded to the base by asuitable adhesive which will not interfere with the transmission of themegasonic energy provided by the transducer 640 and propagated throughthe central wall 634 b and the base 605 of the probe.

[0080] The base 605 can have a frusto-conical configuration just as therear portion of the probe in FIG. 12, and the spring 643 could thenengage the sloping side wall of such shape rather than having the stepconfiguration shown in FIG. 13. Also, in theory, the rod 606 could havea tapered end and the spring could engage it as suggested by FIG. 12.

[0081] A primary purpose of having a probe made of two differentportions is that one portion can be made of a different material fromthe other. For example, the base 605 can be utilized in any cleaningoperation since it does not contact the cleaning solution; however, therod 606 must be compatible with the cleaning solution. Thus, if thecleaning solution is compatible with quartz, a one-piece arrangementsuch as that illustrated in FIG. 1 or FIG. 12 could be convenientlyutilized. If, however, the cleaning solution is not compatible withquartz, such as a solution containing hydrofluoric acid, a material forthe rod is needed that is compatible, such as vitreous carbon, while thebase can be quartz. It is currently difficult to obtain vitreous carbonin a shape such as that illustrated in FIG. 12. However, a straightcylindrical rod is more readily available. Hence, it is practical toutilize it in the arrangement illustrated in FIG. 13. Of course anyother desirable combination of suitable materials for the rod and thebase may be employed.

[0082] As mentioned above, the arrangement of FIG. 13 is particularlydesirable from the standpoint that the transmission of megasonic energyis efficient through the thin wall portion of the heat exchange member,but yet the heat exchange process is very efficient. This is because thetransducer, which is the heat generator, is in direct contact with theheat transfer member, which is in direct contact with the coolantpassage 636. It should be recognized that other heat transferarrangements may be employed. For example, if the heat transfer memberhas sufficient surface area, it might be possible to have it air-cooledrather than liquid-cooled. It should also be recognized that variousother modifications of that type may be made to the embodimentsillustrated without departing from the scope of the invention, and allsuch changes are intended to fall within the scope of the invention, asdefined by the appended claims.

What is claimed is:
 1. An apparatus for processing a substrate,comprising: a support for supporting the substrate in a substantiallyhorizontal orientation; a first source for applying liquid to one sideof the substrate; a second source for applying liquid to an oppositeside of the substrate; and a transmitter for applying sonic energy tothe substrate
 2. The apparatus of claim 1, wherein said first source isa conduit.
 3. The apparatus of claim 2, wherein said second source is aconduit.
 4. The apparatus of claim 1, wherein said first source is asprayer.
 5. An apparatus for cleaning a semiconductor wafer, comprising:means for applying liquid to top and bottom sides of the wafer; and atransmitter for applying megasonic energy to the wafer through theliquid on one of said sides.
 6. Apparatus for cleaning a thin articlehaving two generally planar flat opposite sides, comprising: a supportfor the article; a conduit for applying fluid to one of said sides; anda transmitter configured to apply vibration to the other one of saidsides with sufficient power to produce vibration in said article and insaid fluid to loosen particles on said one side.
 7. The apparatus ofclaim 6, including a conduit for applying cleaning fluid to said otherside adjacent said transmitter to couple the vibration of thetransmitter through the fluid applied to said other side so as to loosenparticles on both sides of the article.
 8. The apparatus of claim 7,wherein said support is configured to support the article in asubstantially horizontal position, and said transmitter is supportedclosely spaced from the article.
 9. The apparatus of claim 6, includinga transducer for vibrating the transmitter and wherein said transmitteris formed of quartz, sapphire, silicon carbide, silicon nitride, quartzcoated with silicon carbide or quartz coated with vitreous carbon. 10.The apparatus of claim 9, including a wall with an opening thereinthrough which gas may be introduced to an area adjacent said transducer.11. The apparatus of claim 9, including a passage of inert gas to purgean area adjacent to said transducer or to cool said transducer.
 12. Theapparatus of claim 9, including an enclosure creating a space adjacentsaid transducer, with an opening in said enclosure for introducing gasinto said space.
 13. The apparatus of claim 6, wherein said support isconfigured to support the article in a substantially horizontal positionand so that the lower side of the article positioned on the support isaccessible so that fluid can be applied to the lower side.
 14. A methodof processing a semiconductor, comprising: transmitting sonic energy tothe wafer while flowing liquid onto both sides of the wafer.
 15. Themethod of claim 14, including positioning a transmitter adjacent to oneside of the wafer to transmit said energy through the liquid to thewafer.
 16. The method of claim 14, wherein said energy is megasonicenergy.
 17. A method for cleaning thin articles having two generallyplanar opposite sides, said method comprising: applying cleaning fluidto one of said sides; and applying energy to the other one of said sideswith sufficient power to produce vibration on said one side in the areaof said cleaning fluid to loosen particles on said one side.
 18. Themethod of claim 17, wherein said energy is applied by applying cleaningfluid to said other side of the article to couple said vibration to thearticle so as to loosen particles on both sides of the article at thesame time.
 19. The method of claim 18, including supporting said articlein substantially a horizontal position.
 20. The method of claim 17,wherein said vibration is at one or more megasonic frequencies.